The present invention relates to a method for on-line calibration of low accuracy voltage sensors through a communication bus. The method of the present invention is particularly useful for calibration of voltage sensors and consequently for voltage measurements in primary and/or secondary distribution electrical sub-stations.
Present solution in primary distribution for voltage measure is well known and is schematically reported in the diagram of FIG. 1. Voltage measure is usually an optional feature, integrated in the bay panel when required by means of standard voltage transformer or voltage sensors. Voltage measurement is normally required for busbar voltage measure on both sides of the circuit breaker and incoming feeders.
Voltage from the secondary winding of the voltage transformer is wired to the analog input of a suitable electronic device to implement the necessary protection, control and metering functions.
Present solutions needs high power voltage transformers in order to supply the information to a high number of devices. This involves also a lot of inter-panel cabling to bring the required information to all the devices.
Voltage measurement is therefore generally carried out when it is aimed at protection functions at a switchboard level, i.e. for under-voltage or over-voltage protection. Using expensive equipments and complicated cabling is much less reasonable and affordable when the voltage information is required for protection functions at a feeder level, such as, for example, for all directional current protection.